Genetics Division, Brigham and Women's Hospital, Harvard Medical School, Boston, MA.
Stem Cell Program, Division of Hematology-Oncology, Boston Children's Hospital, Harvard Medical School, Boston, MA.
Hepatology. 2020 Nov;72(5):1786-1799. doi: 10.1002/hep.31184.
During liver development, bipotent progenitor cells differentiate into hepatocytes and biliary epithelial cells to ensure a functional liver required to maintain organismal homeostasis. The developmental cues controlling the differentiation of committed progenitors into these cell types, however, are incompletely understood. Here, we discover an essential role for estrogenic regulation in vertebrate liver development to affect hepatobiliary fate decisions.
Exposure of zebrafish embryos to 17β-estradiol (E2) during liver development significantly decreased hepatocyte-specific gene expression, liver size, and hepatocyte number. In contrast, pharmacological blockade of estrogen synthesis or nuclear estrogen receptor (ESR) signaling enhanced liver size and hepatocyte marker expression. Transgenic reporter fish demonstrated nuclear ESR activity in the developing liver. Chemical inhibition and morpholino knockdown of nuclear estrogen receptor 2b (esr2b) increased hepatocyte gene expression and blocked the effects of E2 exposure. esr2b mutant zebrafish exhibited significantly increased expression of hepatocyte markers with no impact on liver progenitors, other endodermal lineages, or vasculature. Significantly, E2-stimulated Esr2b activity promoted biliary epithelial differentiation at the expense of hepatocyte fate, whereas loss of esr2b impaired biliary lineage commitment. Chemical and genetic epistasis studies identified bone morphogenetic protein (BMP) signaling as a mediator of the estrogen effects. The divergent impact of estrogen on hepatobiliary fate was confirmed in a human hepatoblast cell line, indicating the relevance of this pathway for human liver development.
Our studies identify E2, esr2b, and downstream BMP activity as important regulators of hepatobiliary fate decisions during vertebrate liver development. These results have significant clinical implications for liver development in infants exposed to abnormal estrogen levels or estrogenic compounds during pregnancy.
在肝脏发育过程中，多能祖细胞分化为肝细胞和胆管上皮细胞，以确保维持机体稳态所需的功能性肝脏。然而，控制定向祖细胞分化为这些细胞类型的发育线索尚不完全清楚。在这里，我们发现雌激素调控在脊椎动物肝脏发育中起着至关重要的作用，以影响肝胆命运决定。
在肝脏发育过程中，用 17β-雌二醇（E2）处理斑马鱼胚胎，显著降低了肝细胞特异性基因表达、肝脏大小和肝细胞数量。相比之下，雌激素合成或核雌激素受体（ESR）信号的药理学阻断增强了肝脏大小和肝细胞标志物的表达。转基因报告鱼显示核 ESR 活性在发育中的肝脏中。化学抑制和核雌激素受体 2b（esr2b）的 morpholino 敲低增加了肝细胞基因表达并阻断了 E2 暴露的影响。esr2b 突变斑马鱼表现出显著增加的肝细胞标志物表达，而对肝脏祖细胞、其他内胚层谱系或脉管系统没有影响。重要的是，E2 刺激的 Esr2b 活性促进胆管上皮细胞分化，而不是肝细胞命运，而 esr2b 的缺失损害了胆管谱系的分化。化学和遗传上位性研究表明，骨形态发生蛋白（BMP）信号作为雌激素作用的介质。雌激素对肝胆命运的不同影响在人肝母细胞瘤细胞系中得到了证实，表明该途径与人类肝脏发育有关。
我们的研究确定了 E2、esr2b 和下游 BMP 活性作为脊椎动物肝脏发育过程中肝胆命运决定的重要调节因子。这些结果对在怀孕期间暴露于异常雌激素水平或雌激素化合物的婴儿的肝脏发育具有重要的临床意义。
